Problem: Solve for $x$ and $y$ using substitution. ${x-3y = 2}$ ${y = -3x-4}$
Explanation: Since $y$ has already been solved for, substitute $-3x-4$ for $y$ in the first equation. ${x - 3}{(-3x-4)}{= 2}$ Simplify and solve for $x$ $x+9x + 12 = 2$ $10x+12 = 2$ $10x+12{-12} = 2{-12}$ $10x = -10$ $\dfrac{10x}{{10}} = \dfrac{-10}{{10}}$ ${x = -1}$ Now that you know ${x = -1}$ , plug it back into $\thinspace {y = -3x-4}\thinspace$ to find $y$ ${y = -3}{(-1)}{ - 4}$ $y = 3 - 4$ $y = -1$ You can also plug ${x = -1}$ into $\thinspace {x-3y = 2}\thinspace$ and get the same answer for $y$ : ${(-1)}{ - 3y = 2}$ ${y = -1}$